Exhaust gas recirculation devices and systems are known in various forms. In recent years, various systems for reducing the emission of pollutants have been presented wherein, in order to improve the combustion, the exhaust gas was recirculated in a cylinder-selective manner. This has been realized by individual flaps that are arranged in individual exhaust-gas recirculation lines leading to the cylinders and that are actuated in common, as is known, e.g., from DE 19842349, as well as by a recirculation of the exhaust gases performed internally of the cylinders or near the cylinders. Such a system is known from DE 10 2005 025 904. In this case, however, additional non-return flaps and several dosing valves have to be provided in the exhaust-gas recirculation lines.
A particular disadvantage in the external recirculation of exhaust gases has been found to reside in the large volumes of exhaust-gas recirculation channels. By the provision of individual throttling members in the exhaust-gas recirculation channels, it has been accomplished to reduce the emission of pollutants because of the possibility of a precise control of the residual gas for each cylinder. However, these known systems are operated with common actuation for all individual exhaust-gas recirculation channels so that, each time, all of the exhaust-gas recirculation lines will be opened synchronously.
A cylinder-selective recirculation system of the above type is disclosed by DE 198 51 922 A1, wherein, downstream of a exhaust-gas return valve, a tube adapted to be rotated by an electric actuator means is arranged in a bore of the suction tube of the internal combustion engine. The tube, acting as a distributor element, is provided with a number of openings via which a connection can be established to an exhaust-gas recirculation channel leading to a suction channel. Thereby, the exhaust gas will be recirculated near the cylinder only at a late point of time, thus avoiding the occurrence of vibrations caused by recirculated exhaust gas in the suction tube that would disturb the charging.
Further, from DE 37 22 048 A1, there is known an exhaust-gas recirculation device comprising a housing accommodating an exhaust-gas inlet channel and a plurality of exhaust-gas outlet channels corresponding in number to the cylinders of the internal combustion engine. Between the exhaust-gas inlet channel and the exhaust-gas outlet channels, a distributor element is arranged in the housing, wherein the distributor element is driven at the rotational speed of the camshaft and has a passage formed therein by which, during rotation of the distributor element, a fluidic connection of the exhaust-gas inlet channel with a respective one of the exhaust-gas outlet channels is established. A phase shift for an upstream or downstream displacement of the exhaust gas, or for adaptation to changed opening times, is not provided.
Known from U.S. Pat. No. 6,308,666 B1 is an internal exhaust gas recirculation system wherein the exhaust gas is recirculated from the outlet valve of a first cylinder to the outlet valve of an adjacent second cylinder. For preventing such a recirculation flow, the connection tube between the two cylinders is provided with a branch while, within the tube downstream of this branch, a rotatable element is arranged for controlling an exhaust gas quantity to be discharged into the atmosphere. The element will rotate at the speed of the camshaft. By means of a phase shifter, the exhaust gas quantity to be recirculated and respectively discharged can be changed.
For further improvement of untreated emission, developments are focusing particularly on variable valve drives which, however, offer only quite complex and thus expensive options for internal control of residual gas. Less expensive state-of-the-art systems for external exhaust gas recirculation, on the other hand, suffer from the disadvantages of insufficient dynamics of the system, and are disadvantageous with respect to the dosing of the recirculated exhaust gas and the assigning of the gas to the individual cylinders.
Thus, there is posed the object of providing an exhaust-gas recirculation device operating in a cylinder-selective and cyclically precise manner, so that exhaust gas can be externally supplied to the individual cylinders respectively at an optimum point of time.